Israel filed a complaint with the United Nations, officials say, though the tanks are not seen as a provocation or an attempt to draw Israel into the fighting.

JERUSALEM — Three Syrian tanks entered a demilitarized zone Saturday along the border with the Golan Heights, spurring Israel to file a complaint with the United Nations, Israeli officials said.

Although the tanks did not enter the Israeli-occupied Golan Heights, Israeli officials said the Syrian military presence is restricted from the border area under a U.N.-monitored cease-fire agreement.

Israeli officials said they did not view the tanks as a provocation or an attempt to draw Israel into the fighting in Syria, where an uprising against President Bashar Assad has devolved into a bitter conflict. But the incident, which came as Syrian tanks battled Syrian rebel forces in the area, underscored how the conflict has been spilling over into neighboring nations.

Turkey and Syria have exchanged cross-border artillery fire, and Syria's frontier with Lebanon has been the site of shelling strikes, gun battles and tit-for-tat kidnappings involving factions on both sides of the Syrian conflict. And it's not the first time violence from Syria's war has drifted into the Golan Heights: In September, errant mortar rounds struck the region.

Meanwhile, in northern Syria on Saturday, rebels launched an assault on a major military air facility, marking the opposition's latest attempt to neutralize the government's air power.

The official Syrian state news agency said that rebels targeted the Taftanaz air base with "heavy weapons and mortars." The state news service reported that troops had "killed a large number of terrorists." There was no immediate word from the opposition on whether the attack had been judged a success.

The government has stepped up airstrikes on various fronts, the opposition says, targeting rebel positions in and around the two largest cities, Damascus and Aleppo.

Syria possesses a large, Soviet-equipped air force and many attack aircraft. Rebel commanders say the government's absolute control of the skies has thwarted their efforts to advance in Aleppo and elsewhere.